U.S. patent application number 10/948892 was filed with the patent office on 2005-12-08 for voltage balancing circuit for multi-cell modules.
This patent application is currently assigned to Maxwell Technologies, Inc.. Invention is credited to Thrap, Guy C..
Application Number | 20050269988 10/948892 |
Document ID | / |
Family ID | 35503836 |
Filed Date | 2005-12-08 |
United States Patent
Application |
20050269988 |
Kind Code |
A1 |
Thrap, Guy C. |
December 8, 2005 |
Voltage balancing circuit for multi-cell modules
Abstract
An energy storage module includes a number of cells coupled in
series between two end terminals, and intermediate terminal or
terminals providing access to one or more junctions between
individual cells of the module. Voltages of the module's cells are
balanced by an intra-module voltage balancer. Two or more such
modules are connected in series. To balance voltages of the
modules, inter-module voltage balancers are used. In one
embodiment, an inter-module voltage balancer is connected to a
junction of two modules and to intermediate terminals of the two
modules. The inter-module balancer attempts to balance voltages of
one or more cells of one of the two modules against one or more
cells of the other module. Through operation of the intra-module
balancers of each module, voltages of both modules are
balanced.
Inventors: |
Thrap, Guy C.; (Del Mar,
CA) |
Correspondence
Address: |
Gregory J. Koerner
Redwood Patent Law
1291 East Hillsdale Boulevard
Suite 205
Foster City
CA
94404
US
|
Assignee: |
Maxwell Technologies, Inc.
San Diego
CA
|
Family ID: |
35503836 |
Appl. No.: |
10/948892 |
Filed: |
September 24, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10948892 |
Sep 24, 2004 |
|
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10860965 |
Jun 4, 2004 |
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Current U.S.
Class: |
320/116 |
Current CPC
Class: |
H02J 7/0016
20130101 |
Class at
Publication: |
320/116 |
International
Class: |
H02J 007/00 |
Claims
I claim:
1. An electric energy storage module, comprising: a first end
terminal and a second end terminal; a plurality of energy storage
cells connected in series between the first end terminal and a
second end terminal to provide voltage output from the first and
the second end terminals; a holder capable of holding the plurality
of energy storage cells; an intra-module voltage balancer capable
of equalizing voltages of the energy storage cells; and at least
one intermediate terminal coupled to one or more common junction of
two of the energy storage cells, wherein the first end terminal,
the second end terminal, and wherein the at least one intermediate
terminal are externally accessible.
2. A module according to claim 1, wherein the holder comprises an
enclosure surrounding and containing the plurality of energy
storage cells and the intra-module voltage balancer.
3. A module according to claim 2, wherein the plurality of energy
storage cells comprises a plurality of double layer capacitors.
4. A module according to claim 2, wherein each energy storage cell
of the plurality of energy storage cells comprises a capacitor.
5. A module according to claim 2, wherein the plurality of energy
storage cells comprises a plurality of secondary cells.
6. A module according to claim 2, wherein the intra-module voltage
balancer comprises a flyback circuit.
7. A module according to claim 2, wherein the intra-module voltage
balancer comprises a shunt balancer.
8. A module according to claim 2, wherein the intra-module balancer
comprises an active balancer.
9. A module according to claim 1, wherein: the at least one
intermediate terminal includes one intermediate terminal coupled to
a first common junction of two of the energy storage cells; and the
first common junction is in the middle of the series of the energy
storage cells so that exactly a first number of energy storage
cells are present between the first common junction and the first
end terminal, and exactly the first number of energy storage
devices are present between the first common junction and the
second end terminal.
10. A module according to claim 9, wherein the first number is
equal to one.
11. A module according to claim 1, wherein: the at least one
intermediate terminal includes a first intermediate terminal
coupled to a first common junction of two of the energy storage
cells, and a second intermediate terminal coupled to a second
common junction of two of the energy storage cells; and a first
number of energy storage cells are present between the first common
junction and the first end terminal, and the first number of energy
storage cells are present between the second common junction and
the second end terminal.
12. A module according to claim 11, wherein the first number is
equal to one.
13. A module according to claim 11, wherein the first number is
greater than one.
14. An energy storage apparatus, comprising: a plurality of energy
storage modules; and one or more inter-module voltage balancer
connected to the plurality of energy storage modules to equalize
voltages of the modules, wherein each module of the plurality of
energy storage modules comprises: a first end terminal and a second
end terminal, a plurality of energy storage cells connected in
series between the first end terminal and a second end terminal of
said each module to provide voltage output from the first and the
second end terminals of said each module, a holder capable of
holding the plurality of energy storage cells of said each module,
an intra-module voltage balancer capable of equalizing voltages of
the energy storage cells of said each module, and at least one
intermediate terminal coupled to one or more common junction of two
of the energy storage cells of said each module; and wherein the
first end terminal, the second end terminal, and the at least one
intermediate terminal of said each module are externally accessible
and connected to the at least one inter-module voltage
balancer.
15. An energy storage apparatus according to claim 14, wherein the
holder of said each module comprises an enclosure surrounding and
containing the plurality of energy storage cells of said each
module and the intra-module voltage balancer of said each
module.
16. An energy storage apparatus according to claim 15, wherein the
inter-module voltage balancer directly equalizes voltages of
combinations of fewer than all cells of said each module, and
indirectly equalizes voltages of the modules.
17. An energy storage apparatus according to claim 15, wherein: the
at least one intermediate terminal of said each module includes one
intermediate terminal coupled to a first common junction of two of
the energy storage cells of said each module; and the first common
junction of said each module is in the middle of the series of the
energy storage cells of said each module so that exactly a first
number of energy storage cells are present between the first common
junction and the first end terminal of said each module, and
exactly the first number of energy storage devices are present
between the first common junction and the second end terminal of
said each module.
18. An energy storage apparatus according to claim 17, wherein the
first number is equal to one.
19. An energy storage apparatus according to claim 17, wherein the
first number is greater than one.
20. An energy storage apparatus according to claim 17, wherein the
plurality of energy storage cells of said each module comprises a
plurality of double layer capacitors.
21. An energy storage apparatus according to claim 15, wherein: the
at least one intermediate terminal of said each module includes a
first intermediate terminal coupled to a first common junction of
two of the energy storage cells of said each module, and a second
intermediate terminal coupled to a second common junction of two of
the energy storage cells of said each module; and a first number of
energy storage cells are present between the first common junction
and the first end terminal of said each module, and the first
number of energy storage cells are present between the second
common junction and the second end terminal of said each
module.
22. An energy storage apparatus according to claim 21, wherein the
first number is equal to one.
23. An energy storage apparatus according to claim 21, wherein the
first number is greater than one.
24. An energy storage apparatus according to claim 21, wherein the
plurality of energy storage cells of said each module comprises a
plurality of double layer capacitors.
25. An energy storage device, comprising: a first module
comprising: a first end terminal and a second end terminal, a first
plurality of energy storage cells connected in series between the
first end terminal and the second end terminal to provide voltage
output from the first and the second end terminals, a first holder
capable of holding the first plurality of energy storage cells, a
first intra-module voltage balancer capable of equalizing voltages
of the energy storage cells of the first plurality, and a first
intermediate terminal coupled to a common junction of two of the
energy storage cells of the first plurality, wherein the first end
terminal, the second end terminal, and the first intermediate
terminal of the first module are externally accessible; a second
module comprising: a third end terminal and a fourth end terminal,
a second plurality of energy storage cells connected in series
between the third end terminal and the fourth end terminal to
provide voltage output from the third and the fourth end terminals,
a second holder capable of holding the second plurality of energy
storage cells, a second intra-module voltage balancer capable of
equalizing voltages of the energy storage cells of the second
plurality, and a second intermediate terminal coupled to a common
junction of two of the energy storage cells of the second
plurality, wherein the third end terminal, the fourth end terminal,
and the second intermediate terminal are externally accessible; and
an inter-module voltage balancer, wherein the first module and the
second module are connected in series so that the second end
terminal of the first module is coupled to the third end terminal
of the second module, and wherein the inter-module voltage balancer
is connected to the second end terminal of the first module, the
first intermediate terminal of the first module, and to the second
intermediate terminal of the second module to equalize directly
voltage of cells located between the first intermediate terminal
and the second end terminal of the first module and voltage of
cells located between the second intermediate terminal and the
third end terminal of the second module.
26. The energy storage device of claim 25, wherein the first holder
comprises a first enclosure surrounding and containing the first
plurality of energy storage cells and the first intra-module
voltage balancer, and the second holder comprises a second
enclosure surrounding and containing the second plurality of energy
storage cells and the second intra-module voltage balancer.
27. The energy storage device of claim 25, wherein the first
plurality of cells comprises a plurality of double layer
capacitors, and the second plurality of cells comprises a plurality
of double layer capacitors.
28. The energy storage device of claim 25, wherein exactly one cell
is located between the first intermediate terminal and the second
end terminal of the first module, and exactly one cell is located
between the second intermediate terminal and the third end terminal
of the second module.
29. The energy storage device of claim 25, wherein exactly the same
number of cells is located between the first intermediate terminal
and the second end terminal of the first module as the number of
cells located between the second intermediate terminal and the
third end terminal of the second module.
30. The energy storage device of claim 29, wherein at least two
cells are located between the first intermediate terminal and the
second end terminal of the first module.
31. A method of equalizing voltages of rechargeable multi-cell
modules with intra-module voltage balancers, the modules being
connected in series, each module comprising a plurality of energy
storage cells connected in series between a first end terminal and
a second end terminal, the method comprising: providing an
inter-module voltage balancer; connecting the inter-module voltage
balancer between two adjacent modules of the plurality of modules;
and operating the inter-module voltage balancer to balance directly
voltages of combinations of fewer than all cells of each module,
thereby equalizing indirectly voltages of the modules.
32. An energy storage device of claim 16, wherein the inter-module
balancer comprises a flyback circuit.
33. An energy storage device of claim 16, wherein the inter-module
balancer comprises a shunt balancer.
34. An energy storage device of claim 16, wherein the inter-module
balancer comprises an active balancer.
35. A energy storage system, comprising: a plurality of modules,
each module comprising a plurality of interconnected double-layer
capacitors; one or more intra-module balancer, wherein between each
double-layer capacitor there is interconnected one intra-module
balancer to equalize voltages of the double-layer capacitors; and
one or more inter-module balancer, wherein between each module
there is interconnected one inter-module balancer to equalize
voltages appearing across the modules.
36. The energy storage system of claim 35, wherein the plurality of
modules comprise an enclosure surrounding and containing the
interconnected double-layer capacitors.
37. The energy storage system of claim 35, wherein the inter-module
balancer equalizes voltages across one or more double-layer
capacitor in one module against voltages across one or more
double-layer capacitor in a second module.
38. The energy storage device of claim 37, wherein the voltages
across the one or more double-layer capacitor is less than the
voltages across the modules.
Description
RELATED APPLICATION
[0001] The present invention is a CIP of commonly assigned U.S.
patent application Ser. No. 10/860,965, filed 4 Jun. 2004, Attorney
Docket No. M111US, from which priority is claimed.
FIELD OF THE INVENTION
[0002] The present invention relates generally to circuits for
balancing voltages, and, more specifically, to circuits for
balancing voltages of multi-cell energy storage modules.
BACKGROUND
[0003] Energy storage devices are often constructed of individual
cells connected in series within a common enclosure or module.
Output terminals typically provide access to the combined voltage
of the series cell combination. Such modules provide nominal
operating voltages higher than those available from each individual
cell. When charging a number of individual energy storage cells
connected in series, different rates of accepting charge and
different voltage responses to the charge can cause some of the
cells to have higher voltages than other cells. Similarly,
discharging a series combination of cells can result in voltage
imbalances from cell to cell. These phenomena are problematic for
at least two related reasons.
[0004] First, excessive voltage (overvoltage) across a cell can
shorten the life of the cell, and, consequently, shorten the life
of the module in which the cell is installed. Overvoltage can also
cause a catastrophic failure of the cell and the module. To avoid
such failures, modules may provide a safety margin, with the
maximum voltage rating of a module set below the sum of the voltage
ratings of the module's constituent cells. This approach lowers the
energy capacity of the module, and may be not entirely
foolproof.
[0005] Second, an overvoltage condition of some cells may cause
lower than average voltage (undervoltage) in other cells. The cells
with low voltages may then accept less energy and, thus, be
underutilized, also resulting in a lower stored energy capacity of
the module.
[0006] It follows that, ideally, all cells of a module should be
identical, so that the cells accept and release electrical charge
at the same rate such that their voltages closely track each other.
In practice, however, cell characteristics vary from cell to cell.
This is particularly true when the cells have not been matched to
each other. But matching cells is an additional step in the
manufacturing process, which may increase the cost of the modules.
Moreover, the original match is hardly ever perfect; the closer the
required match, the costlier the matching step becomes. And even
closely-matched cells may age differently, with increasing
divergence in their performance characteristics over both
charge-discharge cycles and chronological age.
[0007] To minimize problems associated with cell imbalance, some
modules employ cell voltage balancers (also known as voltage
equalizers) across the cells to help keep the cell-to-cell voltage
variations within a module relatively low. In this document, such
balance will be referred to as intra-module voltage balance.
[0008] Individual modules may themselves also be connected in
series to achieve operating voltages higher than those available
from each individual module. In practice, for reasons similar to
those that cause cell-to-cell voltage variations discussed above,
each module may exhibit different operating characteristics. Thus,
module-to-module voltage imbalance (inter-module imbalance) may
arise, whereby some modules may have higher voltages than other
modules. If identical modules could be selected for the series
combination, the voltages across each module would likely be about
the same. Such balance will be referred to as inter-module
balance.
[0009] Although overvoltage of the individual constituent cells may
be avoided, in some circumstances, because of the presence in the
modules of internal cell voltage balancers (i.e., intra-cell
voltage balancers), module-to-module voltage imbalance may
nevertheless occur. For example, inter-module imbalance may limit
the total voltage and energy available from the series combination
of the modules, and reduce energy efficiency of the series
combination of modules. Moreover, certain cell voltage balancers
might not prevent cell overvoltage if the entire module is
overcharged. To reduce the problems associated with
module-to-module voltage imbalance, conventional voltage balancers
can be used to balance multiple modules against each other in a way
that is similar to the use of voltage balancers to equalize
voltages of the individual cells. Two related problems, however,
arise when implementing such balancing in practice.
[0010] First, the module voltage balancers (inter-module voltage
balancers) used in such applications need to be rated for the full
voltage available from a module. When the module includes two
individual cells, for example, the voltage rating is twice that of
each individual cell. Often, modules include a large number of
cells, resulting in commensurately higher required voltage
ratings.
[0011] Second, even assuming the same balancing current for a
module as that for an individual cell, the power rating of each
module balancer increases by the same factor as the voltage rating.
Thus, a voltage balancing circuit designed to balance 50-volt
modules using 300 milliamperes should be capable of handling
fifteen watts. This problem naturally increases with increasing
currents, which can be important when balancers are also used to
charge modules using cells capable of receiving high currents, such
as modules built with double layer capacitor cells.
[0012] Thus, when voltage balancer techniques are applied to
module-to-module voltage balancing, cost, size, and performance
characteristics that are undesirable need to be addressed.
SUMMARY
[0013] A need thus exists for multi-cell modules capable of being
equalized using voltage balancers with relatively low voltage and
low power rated components. Another need exists for multi-cell
module balancing techniques using voltage balancers with relatively
low voltage and power rated components. A further need exists to
provide voltage balancers that can be constructed with components
having relatively low voltage and power ratings, but capable of
balancing multi-cell modules.
[0014] The present invention is directed to an electric energy
storage module that includes first and second end terminals, a
plurality of energy storage cells connected in series between the
first and second end terminals to provide voltage output from the
end terminals, a holder capable of holding the plurality of energy
storage cells, an intra-module voltage balancer capable of
equalizing voltages of the energy storage cells, and an
intermediate terminal coupled to a common junction of two of the
energy storage cells. The intermediate terminal and the end
terminals are externally accessible.
[0015] In various embodiments of the module, the cells include
capacitors, such as double layer capacitors, and other rechargeable
cells. The holder can be an enclosure containing the cells and the
intra-module voltage balancer. The intra-module balancer can
include a flyback circuit or a shunt balancer. The intermediate
terminal can be coupled in the middle of the series of the energy
storage cells, so that exactly the same number of energy storage
cells are present between the intermediate terminal and each of the
end terminals. In some embodiments, two intermediate terminals are
present, each intermediate terminals being connected to a different
junction of two of the energy storage cells. The same number of
energy storage cells can be present between each intermediate
terminal and the end terminal nearest the intermediate terminal.
More than two intermediate terminals are present in some
embodiments.
[0016] The present invention is also directed to energy storage
apparatus built with a plurality of energy storage modules, such as
the modules described above. The modules are connected in series
and their voltages are equalized by one or more inter-module
voltage balancers. In one embodiment, the inter-module balancer is
coupled to the junctions of adjacent modules, and to the
intermediate terminals of the modules.
[0017] In operation, the inter-module balancer equalizes voltages
of a subset of one or more cells of each module. Because the
intra-module balancers (internal to the modules) attempt to
equalize the voltages of all cells of a given module, equalizing
voltages of subsets of the cells tends to equalize the voltages of
the entire modules.
[0018] In one embodiment, an electric energy storage module
comprise a first end terminal and a second end terminal; a
plurality of energy storage cells connected in series between the
first end terminal and a second end terminal to provide voltage
output from the first and the second end terminals; a holder
capable of holding the plurality of energy storage cells; an
intra-module voltage balancer capable of equalizing voltages of the
energy storage cells; and at least one intermediate terminal
coupled to one or more common junction of two of the energy storage
cells; wherein the first end terminal, the second end terminal, and
the at least one intermediate terminal are externally accessible.
The holder may comprise an enclosure surrounding and containing the
plurality of energy storage cells and the intra-module voltage
balancer. The plurality of energy storage cells may comprise a
plurality of double layer capacitors. Each energy storage cell of
the plurality of energy storage cells may comprise a capacitor. The
plurality of energy storage cells may comprise a plurality of
secondary cells. The intra-module voltage balancer comprises a
flyback circuit. The intra-module voltage balancer may comprise a
shunt balancer. The intra-module balancer may comprise an active
balancer. The at least one intermediate terminal may include one
intermediate terminal coupled to a first common junction of two of
the energy storage cells, wherein the first common junction is in
the middle of the series of the energy storage cells so that
exactly a first number of energy storage cells may be present
between the first common junction and the first end terminal, and
wherein exactly the first number of energy storage devices may be
present between the first common junction and the second end
terminal. The first number may be equal to one. The at least one
intermediate terminal may include a first intermediate terminal
coupled to a first common junction of two of the energy storage
cells, and a second intermediate terminal coupled to a second
common junction of two of the energy storage cells, wherein a first
number of energy storage cells may be present between the first
common junction and the first end terminal, and wherein the first
number of energy storage cells may be present between the second
common junction and the second end terminal. The first number may
equal to one. The first number may be greater than one.
[0019] In one embodiment, an energy storage apparatus comprises a
plurality of energy storage modules; and one or more inter-module
voltage balancer connected to the plurality of energy storage
modules to equalize voltages of the modules; wherein each module of
the plurality of energy storage modules comprises a first end
terminal and a second end terminal, a plurality of energy storage
cells connected in series between the first end terminal and a
second end terminal of said each module to provide voltage output
from the first and the second end terminals of said each module, a
holder capable of holding the plurality of energy storage cells of
said each module, an intra-module voltage balancer capable of
equalizing voltages of the energy storage cells of said each
module, and at least one intermediate terminal coupled to one or
more common junctions of two of the energy storage cells of said
each module; and wherein the first end terminal, the second end
terminal, and the at least one intermediate terminal of said each
module are externally accessible and connected to the at least one
inter-module voltage balancer. The holder of said each module may
comprise an enclosure surrounding and containing the plurality of
energy storage cells of said each module and the intra-module
voltage balancer of said each module. The inter-module voltage
balancer may equalize voltages of combinations of fewer than all
cells of said each module, and indirectly equalize voltages of the
modules. The at least one intermediate terminal of said each module
includes one intermediate terminal coupled to a first common
junction of two of the energy storage cells of said each module,
wherein the first common junction of said each module is in the
middle of the series of the energy storage cells of said each
module so that exactly a first number of energy storage cells are
present between the first common junction and the first end
terminal of said each module, and wherein exactly the first number
of energy storage devices are present between the first common
junction and the second end terminal of said each module. The first
number may equal to one. The first number may be greater than one.
The plurality of energy storage cells of said each module may
comprise a plurality of double layer capacitors. The at least one
intermediate terminal of said each module may include an
intermediate terminal coupled to a first common junction of two of
the energy storage cells of said each module, and a second
intermediate terminal coupled to a second common junction of two of
the energy storage cells of said each module; wherein a first
number of energy storage cells are present between the first common
junction and the first end terminal of said each module, and
wherein the first number of energy storage cells are present
between the second common junction and the second end terminal of
said each module. The first number may equal to one. The first
number may be greater than one. The inter-module balancer may
comprise a flyback circuit. The inter-module balancer may comprise
a shunt balancer. The inter-module balancer may comprise an active
balancer. The plurality of energy storage cells of said each module
may comprise a plurality of double layer capacitors.
[0020] In one embodiment, an energy storage device comprises a
first module comprising a first end terminal and a second end
terminal, a first plurality of energy storage cells connected in
series between the first end terminal and the second end terminal
to provide voltage output from the first and the second end
terminals, a first holder capable of holding the first plurality of
energy storage cells, a first intra-module voltage balancer capable
of equalizing voltages of the energy storage cells of the first
plurality, and a first intermediate terminal coupled to a common
junction of two of the energy storage cells of the first plurality,
wherein the first end terminal, the second end terminal, and the
first intermediate terminal of the first module are externally
accessible; a second module comprising a third end terminal and a
fourth end terminal, a second plurality of energy storage cells
connected in series between the third end terminal and the fourth
end terminal to provide voltage output from the third and the
fourth end terminals, a second holder capable of holding the second
plurality of energy storage cells, a second intra-module voltage
balancer capable of equalizing voltages of the energy storage cells
of the second plurality, and a second intermediate terminal coupled
to a common junction of two of the energy storage cells of the
second plurality, wherein the third end terminal, the fourth end
terminal, and the second intermediate terminal are externally
accessible; and an inter-module voltage balancer; wherein the first
module and the second module are connected in series so that the
second end terminal of the first module is coupled to the third end
terminal of the second module; and the inter-module voltage
balancer is connected to the second end terminal of the first
module, the first intermediate terminal of the first module, and to
the second intermediate terminal of the second module to equalize
directly voltage of cells located between the first intermediate
terminal and the second end terminal of the first module and
voltage of cells located between the second intermediate terminal
and the third end terminal of the second module. The first holder
may comprise a first enclosure surrounding and containing the first
plurality of energy storage cells and the first intra-module
voltage balancer, and the second holder may comprise a second
enclosure surrounding and containing the second plurality of energy
storage cells and the second intra-module voltage balancer. The
first plurality of cells may comprise a plurality of double layer
capacitors, and the second plurality of cells may comprise a
plurality of double layer capacitors. One cell may be located
between the first intermediate terminal and the second end terminal
of the first module, and one cell may be located between the second
intermediate terminal and the third end terminal of the second
module. Exactly the same number of cells may be located between the
first intermediate terminal and the second end terminal of the
first module as the number of cells located between the second
intermediate terminal and the third end terminal of the second
module. At least two cells may be located between the first
intermediate terminal and the second end terminal of the first
module.
[0021] In one embodiment, a method of equalizing voltages of
rechargeable multi-cell modules with intra-module voltage balancers
includes the modules being connected in series, each module
comprising a plurality of energy storage cells connected in series
between a first end terminal and a second end terminal, the method
comprising providing an inter-module voltage balancer; connecting
the inter-module voltage balancer junctions between two adjacent
modules of the plurality of modules; and operating the inter-module
voltage balancer to balance directly voltages of combinations of
fewer than all cells of each module, thereby equalizing indirectly
voltages of the modules.
[0022] In one embodiment, an energy storage system comprises a
plurality of modules, each module comprising a plurality of
interconnected double-layer capacitors; one or more intra-module
balancer, wherein between each double-layer capacitor there is
interconnected one intra-module balancer to equalize voltages of
the double-layer capacitors; and one or more inter-module balancer,
wherein between each module there is interconnected one
inter-module balancer to equalize voltages appearing across the
modules. The energy storage system may comprise an enclosure
surrounding and containing the interconnected double-layer
capacitors. The inter-module balancer may equalize voltages across
one or more double-layer capacitor in one module against voltages
across one or more double-layer capacitor in a second module. The
voltages across the one or more double-layer capacitor may be less
than the voltages across the modules.
[0023] These and other features and aspects of the present
invention will be better understood with reference to the following
description, drawings, and appended claims.
BRIEF DESCRIPTION OF THE FIGURES
[0024] FIG. 1 illustrates selected elements of a two-cell energy
storage module, in accordance with aspects of the present
invention;
[0025] FIG. 2 illustrates selected elements of an energy storage
module with more than two cells, in accordance with aspects of the
present invention;
[0026] FIG. 3A illustrates selected elements of a combination of
four multi-cell energy storage modules coupled in series and
balanced with inter-module voltage balancers, according to aspects
of the present invention;
[0027] FIG. 3B illustrates selected interconnections of the
combination of FIG. 3A;
[0028] FIG. 4 illustrates selected elements of a combination of
energy storage modules with an inter-module voltage balancer, in
accordance with aspects of the present invention;
[0029] FIG. 5 illustrates selected elements of another combination
of energy storage modules with an inter-module voltage balancer, in
accordance with aspects of the present invention; and
[0030] FIG. 6 illustrates selected elements of a combination of
multi-cell modules with a flyback circuit used for inter-module
voltage balancing, in accordance with aspects of the present
invention.
DETAILED DESCRIPTION
[0031] Reference will now be made in detail to several embodiments
of the invention that are illustrated in the accompanying drawings.
Same or similar reference numerals may be used in the drawings and
the description to refer to the same or like parts. The drawings
are in a simplified form and not to precise scale. For purposes of
convenience and clarity, directional terms such as top, bottom,
left, right, up, down, over, above, below, beneath, rear, and front
may be used with respect to the accompanying drawings. These and
similar directional terms should not be construed to limit the
scope of the invention in any manner.
[0032] In this description, the words "embodiment" and "variant"
refer to a particular apparatus or process, and not necessarily to
the same apparatus or process. Thus, "one embodiment" (or a similar
expression) used in one place or context can refer to a particular
apparatus or process; the same or a similar expression in a
different place can refer to a different apparatus or process. The
expression "alternative embodiment" and similar phrases are used to
indicate one of a number of possible embodiments. The number of
possible embodiments is not limited. The words "couple," "connect,"
and similar terms with their inflectional morphemes are used
interchangeably, unless the difference is noted or otherwise made
clear from the context. These words and expressions do not
necessarily signify direct connections, but include connections
through mediate components and devices. The word "module" may be
used interchangeably with other equivalent terms to signify a unit
of energy storage cells coupled within a common holder (e.g., an
enclosure or another device for holding the cells together) that
has output terminals for providing access to the combined voltage
of the cell combination. Additional definitions and clarifications
may be interspersed in the text of this document.
[0033] FIG. 1 is a high-level illustration of a two-cell energy
storage module 100 in accordance with aspects of the present
invention. The module 100 includes two individual energy storage
cells 120A and 120B coupled in series between a positive end
terminal 140 and a negative end terminal 150. An intermediate
terminal 160 is coupled to the junction between the individual
energy storage cells 120A and 120B. Reference numeral 130
designates an intra-module voltage balancer, which is coupled
across each of the individual energy storage cells 120A and 120B.
The voltage balancer 130 and the energy cells 120 are surrounded
and contained in an enclosure 110. The terminals 140, 150, and 160
are accessible from outside of the enclosure 110 and can be used to
couple the module 100 to external devices. In operation, the module
100 is charged through the terminals 140 and 150, and then provides
energy through the same terminals during discharge cycles. The
intra-module voltage balancer 130 maintains approximate voltage
balance between the individual energy storage cells 120A and
120B.
[0034] In the illustrated embodiment, the cells 120A and 120B are
double layer capacitor cells, which are known for their high
capacitance per unit weight and per unit volume. Double layer
capacitors are also known as ultracapacitors or supercapacitors.
Generally, modules used in accordance with embodiments of the
present invention can include double layer capacitor cells as well
as energy storage cells built with other technologies. For example,
capacitive cells built with conventional technologies, and
electrochemical and other secondary (rechargeable) cells can be
used for constructing modules.
[0035] The intra-module voltage balancer 130 can be, for example,
an active balancer, a shunt balancer, or a flyback circuit
balancer. An active balancer is described in currently pending
commonly assigned patent application Ser. No. 10/423,708, Docket
No. 501, which is incorporated herein by reference.
[0036] A shunt balancer can provide a controlled parallel
connection across an individual cell to limit current into the cell
(or drain current form the cell) under certain conditions, such as
when the voltage of the cell exceeds a predetermined level. For
example, voltage across an individual cell can be compared,
directly or indirectly, to a voltage generated by a stable voltage
reference, and a solid state switch can be opened or closed
depending on the result of the voltage comparison. When the
comparison indicates an overvoltage condition, the switch is
closed, shunting the current between the cell's terminals. many
shunt circuits and variations thereof are known to those skilled in
the art.
[0037] A flyback balancer can include a transformer with a primary
winding and a plurality of substantially identical secondary
windings. Each secondary winding is connected across one of the
module's cells. To prevent the cells from discharging through their
associated windings, diodes are inserted in series with the
windings. A power source for charging the module is then connected
to the primary winding through a switch. The state of the switch is
controlled by an alternating signal from an oscillator. When the
oscillator causes the switch to open, magnetic energy stored in the
transformer core "flies" into the individual cells, with more
energy charging the cells that have low voltages. The cell voltages
thus are brought into balance.
[0038] In some embodiments, the voltage balancer 130 acts during
charge cycles only. In other embodiments, the voltage balancer 130
acts during both charge and discharge cycles, for example, as
described in currently pending commonly assigned patent application
Ser. No. 10/860,965, Docket No. M113US, which describes a novel
variant of a flyback balancer circuit and which is incorporated
herein by reference. Embodiments with voltage balancers that
operate only during discharge cycles, only during storage periods,
or during any combination of storage periods and charge and
discharge cycles, thus, fall within the scope of the present
invention.
[0039] FIG. 2 is a high-level illustration of an N-cell energy
storage module 200 where N is greater than two, in accordance with
aspects of the present invention. In this embodiment, N individual
energy storage cells 220, through 22N are coupled in series between
a positive end terminal 240 and a negative end terminal 250. A
voltage balancer 230 includes connections that couple the voltage
balancer 230 across each of the individual energy storage cells
220. The voltage balancer 230 equalizes the voltages of the
individual cells 220, bringing these voltages into approximate
balance. An intermediate terminal 260A is coupled to the junction
between the cells 220, and 2202. Similarly, an intermediate
terminal 260B is coupled to the junction between the cells
220.sub.N and 220.sub.N-1. The cells 220 and the voltage balancer
230 are contained in an enclosure 210. The terminals 240, 250,
260A, and 260B are externally accessible. This embodiment does not
contain external connections to junctions between the individual
cells 220, except for the intermediate terminals 260A and 260B.
Other embodiments may include such connections.
[0040] FIG. 3A is a high-level illustration of a combination 300 of
four multi-cell energy storage modules 304, 308, 312, and 316
coupled in series and balanced with inter-module balancers 324,
328, and 332, according to aspects of the present invention.
[0041] Each of the energy storage modules 304, 308, 312, and 316
includes a number of individual energy storage cells coupled in
series between a pair of external end terminals. The external end
terminals are designated with reference numerals 304A, 304B, 308A,
308B, 312A, 312B, 316A, and 316B. Each module further includes one
or more intra-module voltage balancer for equalizing the voltages
of the individual cells. The individual cells, the intra-module
voltage balancers, and internal module interconnections are not
specifically shown in the Figure, but are similar to those
illustrated in FIG. 2, and should be understood by a person skilled
in the appropriate art. Each module also includes a pair of
intermediate terminals. The intermediate terminals illustrated in
FIG. 3A include terminals 304C, 304D, 308C, 308D, 312C, 312D, 316C,
and 316D.
[0042] In the embodiment of FIG. 3A, each intermediate terminal of
a module is separated from an end terminal of the module by one
cell. For example, one cell is coupled between terminals 304A and
304C, and one cell is coupled between terminals 304B and 304D. The
same arrangement exists in the modules 308, 312, and 316. Note that
in embodiments where each module includes only two cells, a single
intermediate terminal suffices; in effect the terminals 304C and
304D would then be combined into the single terminal. Such module
100 was illustrated in FIG. 1 and discussed above. As will be seen
from the discussion accompanying FIG. 5, a single intermediate
terminal can be used even where each module includes more than two
cells.
[0043] The combination 300 further includes three inter-module
voltage balancers, which are designated with reference numerals
324, 328, and 332. The inter-module balancers 324, 328, and 332 may
be of an active, shunt, flyback circuit configuration as described
herein. The inter-module balancers 324, 328, and 332 help to bring
the voltages output by each of the modules 304, 308, 312, and 316
into approximate balance, i.e., into approximate parity with each
other.
[0044] To help describe operation of the combination 300, FIG. 3B
illustrates in more detail interconnections of the inter-module
voltage balancer 324, and the modules 304 and 308. Note that end
cell 305 of the module 304 is connected between the terminals 304B
and 304D of that module. Similarly, end cell 309 of the module 308
is connected between the terminals 308A and 308C of the same
module. The inter-module balancer 324 is connected so that its
common terminal 324A is coupled to the common junction of the
modules 304 and 308, i.e., to the terminals 304B and 308A.
Terminals 324B and 324C of the balancer 324 are connected to the
intermediate terminals 304D and 308C, respectively. Thus, the
balancer 324 is positioned so that it can balance the voltages of
the cells 305 and 309 against each other. For example, the balancer
324 can transfer energy from the cell with the higher voltage into
the cell with the lower voltage.
[0045] The inter-module balancer 324 is not the only device
affecting the voltages on the cells 305 and 309. Recall that the
cells 305 and 309 are also connected to intra-module voltage
balancers; in FIG. 3B, these intra-module balancers are designated
with reference numerals 306 and 310, respectively. Although
inter-module balancer 324 increases or decreases the cell voltage
of cells 305 and 309, intra-module balancers 306 and 310 also act
to increase or decrease the voltages of cells (including cells 305
and 309) within the modules. Voltage balance among cells within a
module is propagated by the intra-module balancers 306 and 310 and
between modules via inter-module balancer 324. Similarly, voltage
imbalances appearing between modules are equalized by inter-module
balancer 324 and, in turn this equalized voltage is propagated by
the inter-module balancers 306 and 310 to cells within a module. In
other words, inter-module balancer 324, by directly balancing
voltages of individual cells 305 and 309 tends to indirectly
balance the voltage of the modules 304 and 308. ("Directly" here
signifies an immediate causal connection between operation of the
inter-module balancer and its effect on the voltages of the
individual cells 305 and 309; "indirectly" signifies causal
connection through operation of intermediate devices, which are
intra-module balancers 306 and 310 in this example.)
[0046] Note that the voltages appearing across the terminal 324A
and either one of the terminals 324B or 324C are essentially
voltages of the cells 305 or 309. Thus, the components of the
inter-module balancer 324 may (but need not) be rated for voltages
less than those that can be sourced by the complete modules 304 or
308.
[0047] Although FIG. 3A illustrates the inter-module voltage
balancers 324, 328, and 332 as separate devices, this is not a
requirement of the invention. Indeed, multiple inter-module
balancers can be advantageously built as a single device. FIG. 4
illustrates a combination 400 of energy storage modules with a
single inter-module voltage balancer. The arrangement of FIG. 4 is
similar to that of FIG. 3A, and most apparatus elements are
designated with the same numerals in the two Figures. In FIG. 4,
however, a single inter-module voltage balancer 424 may be
configured to perform the module voltage equalization performed by
balancers 324, 328, and 332 in the embodiment of FIG. 3A.
[0048] In the embodiments described above, a single cell is coupled
between each intermediate terminal and the nearest end terminal of
a module. See, for example, cells 305 and 309 in FIG. 3B. This,
however, is not a requirement of the invention. FIG. 5 shows
adjacent multi-cell modules 570 and 580 of a combination 500. The
module 570 includes six energy storage cells (572, 573, 574, 575,
576, and 577) coupled in series between end terminals 578A and
578B. Intermediate terminal 578C connects to the common junction of
the middle cells 574 and 575. An intra-module voltage balancer 571
equalizes the voltages of the individual cells 572 through 577.
Layout of the module 580 is the same as that of the module 570.
Here, the cells are designated with reference numerals 582 through
587, the intra-module balancer is designated with numeral 581, the
intermediate terminal is designated as 588C, and the end terminals
are designated as 588A and 588B. An inter-module voltage balancer
524 connects to the intermediate terminals 578C and 588C, and to
the common junction of the modules 570 and 580.
[0049] In operation, each of the intra-module balancers 571 and 581
equalizes the cell voltages within its respective module. At the
same time, the inter-module balancer 524 attempts to equalize
(directly) the combined voltage of the cells 575, 576, and 577
against the combined voltage of the cells 582, 583, and 584.
Intuitively, this is similar to equalizing voltages of a single
cell of one of the modules and a single cell of the other module,
as was described above with reference to FIG. 3B. In essence,
decreasing or increasing the combined voltage of each trio of cells
(575/576/577 and 582/583/584) tends, over time, to increase or
decrease the combined voltages of all cells within the respective
modules through operation of the intra-cell voltage balancers 571
and 581. In this way, the inter-module voltage balancer 524 tends
to balance indirectly the voltages of the modules 570 and 580.
[0050] Various voltage balancing schemes can be used for
constructing inter-module balancers, such as balancers 324, 424,
and 524 discussed above. One exemplary embodiment uses a flyback
circuit for this purpose. FIG. 6 illustrates a combination 600 of
multi-cell modules 670 and 680 with such a flyback circuit 690. The
flyback circuit 690 includes a transformer 693 with a core 693A,
primary winding 693B and secondary windings 693C and 693D. The
primary winding 693B is coupled in series with a solid state switch
692, such as a field effect transistor (FET) device. The series
combination of the primary winding 693B and the switch 692 is
coupled across intermediate terminals 678C and 688C of the modules
670 and 680. Each of the secondary windings 693C and 693D is
coupled in series with a blocking diode 694 and 695. The
diode-winding combinations are coupled in series with each other
and across the terminals 678C and 688C. The common junction of the
modules 670 and 680 (terminals 678B and 688A) is connected to the
common junction of the two diode-winding combinations, between the
diode 694 and the secondary winding 693C, as shown in FIG. 6. An
oscillator 691 generates a signal that drives the input of the
switch 692, periodically changing the state of the switch 692 from
open to closed, and vice versa.
[0051] When the switch 692 is closed, the series combination of the
primary winding 693B and the switch 692 is effectively connected
across the terminals 678C and 688C. Thus, current sourced by the
cells of the modules 670 and 680 begins to flow through the primary
winding 693B. As the current increases, electric energy is
converted into magnetic field energy stored in the transformer core
693A. At some point, the signal output by the oscillator 691
changes to a level that closes the switch 692. The current flow
through the primary winding 693B then quickly diminishes and then
stops completely. As a result, the magnetic field of the core 693A
collapses, and the energy stored in the field "flies back" into
secondary windings 693C and 693D, inducing voltages across each of
these secondary windings. These induced voltages flow through
blocking diodes 694 and 695 into the cells of the modules 670 and
680.
[0052] Because the secondary windings 693C and 693D and the primary
winding 693B are magnetically coupled together, more energy tends
to flow into the cell (or cells) with a relatively low voltage than
into the cell (or cells) with a relatively high voltage.
[0053] The signal output by the oscillator 691 alternately opens
and closes the switch 692, causing the cycles of storing energy in
the magnetic field and releasing the stored energy into the
secondary windings 693C and 693D to repeat, balancing the voltages
of the cells in the process. Because of the presence of
intra-module balancers (not shown in FIG. 6), equalizing the
voltage of selected cells of the module 670 against the voltage of
selected cells of the module 680 tends to equalize the total
voltages of the two modules.
[0054] At times when no voltage is induced in the secondary
windings 693C and 693D, the blocking diodes 694 and 695 prevent the
module cells from discharging through these windings.
[0055] This document describes in some detail inventive multi-cell
modules, voltage balancing circuits, and methods for balancing
voltages of multi-cell modules. This was done for illustration
purposes. Neither the specific embodiments of the invention as a
whole, nor those of its features limit the general principles
underlying the invention. In particular, the invention is not
limited to the specific components described, or to particular
applications. The specific features described herein may be used in
some embodiments, but not in others, without departure from the
spirit and scope of the invention as set forth. Many additional
modifications are intended in the foregoing disclosure, and it will
be appreciated by those of ordinary skill in the art that in some
instances some features of the invention will be employed in the
absence of a corresponding use of other features. The illustrative
examples therefore do not define the metes and bounds of the
invention and the legal protections afforded the invention, which
function is served by the claims and their legal equivalents.
* * * * *